Apparatus for through ringing on telephone trunk-lines.



PATENTED OCT. 25, 1904.

H. M. CRANE. APPARATUS FOR THROUGH RINGING 0N TELEPHONE TRUNK LINES.

APPLICATION FILED FEB. 17. 1902.

N0 MODEL.

' ATTORNEY last-mentioned board.

" UNITED STATES Patented October 25, 1904.

PATENT Orrrca.

HENRY M. CRANE, OF NEW YORK, N. Y., ASSIGNOR, TO I/VESTERN ELECTRICCOMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

APPARATUS FQR THROUGH RINGING ON TELEPHONE-TRUNK-LINES.

SPECIFICATION forming part of Letters Patent N 0. 772,927, dated October25, 1904.

i Application filed February 1'7, 1902. Serial No. 94,381. (No model.)

T0 at whom it may concern):

Be it known that I, HENRY M. CRANE, a citizen of the UnitedStates,'residing at New York,

in the county of New York and State of New York, have invented a certainnew and useful Improvement in Apparatus for Through Ringing on TelephoneTrunk-Lines, of which the following is a full, clear, concise, and exactdescription.

My invention relates to trunk-lines for telephone-exchanges, and has forits object to pro vide improved apparatus and circuits whereby anoperator at one terminal of a trunk-line may signal directly thesubstation of a telephone-line which is connected to the other terminalthereof.

In long trunk-lines it is usual to provide a repeating-coil at one ofthe switchboards which divides the trunk-line into two sections unitedtelephonically through the windings of the coil. One section extends tothe distant board and the other to the terminal at the local board,which is adapted for connection with subscribers lines.

In telephone systems as usually constructed the trunk-line extends froma spring-jack terminal at the answering-switchboard to a plug terminalat the trunking-board, the repeatingcoil being interposed in thetrunk-line at the It is desirable that the operator at the answering orlong-distance board who supervises the connection should be able tosignal the called station directly through the trunk-line without beingobliged to call upon the trunk operator at the distant end of thetrunk-line for assistance; but ringing cannot be successfully done fromthe answering-switchboard through the repeating-coil for variousreasons, and it has been usual heretofore for the trunk-operator at thereceiving-switchboard to ring the called station at the time of puttingup the connection upon the order of the long-distance operator. Thisdivision of the work of establishing and supervising the connectioncauses considerable confusion and loss of time, which is increased whenthe called party does not answer the first signal and requires to berung a second time.

For the purpose of operating automatic disconnect-signals on longtrunk-lines it has been customary to use both line conductors as onelimb of an earth-completed circuit, ground branches being connected ateach end of the trunk-line with both of the line conductors.

By including a source of current and the sigrial controlling magnets inthese ground branches the necessity of running a third conductor inassociation with the trunk-line to carry currents is avoided.

My invention is especially designed for application to asystem whereinthe two line conductors of the trunk-line are used in multiple toconstitute one limb of the signal-circuit, as above indicated, and bymeans of my said invention such system may readily be equipped to permitthe supervising operator at one end of the trunk-line to ring the calledparty directly by manipulating a ringing-key in the usual way instead ofcalling upon the trunking operator to do the ringing. My scheme is toprovide an automatic ringing-key at the trunking-board controlledthrough the agency of amagnet which has two windings conductivelyconnected, respectively,between the two limbs of the trunk-lineand theearth or other return conductor. At the distant end of the trunk-linethe two limbs thereof are connected through resistances to the earth orreturn conductor, and a signal-circuit is thus established over the lineconductors in multiple, in the undivided portion of which circuit thesignal devices and source of current may be included.

The two windings of the magnet which controls the ringing-keyarearranged to act differentially under the influence of the signalcurrentwhich flows through them in multiple, so that the ringing-key is notactuated thereby; but the supervising operator at the distant end of thetrunk-line is provided with a calling-key which is adapted to alter theflow of current in one of the windings of the differential magnet, as'by connecting one of the line conductors of the trunk-line directly tothe earth or return conductor. The differential magnet is thusunbalanced and brings about the operation of the local ringing-key.whereby a suitable source of ringing-current is automatically applied tothe called line.

1 will describe my invention more particularly by reference to theaccompanying drawing, which is a diagram showing an ordinarytelephone-line extending from a substation to a central-office answeringor long-distance switchboard and there connected, through thesupervising-operatofis plug-circuit, with a trunk-line extending to atrunking-board.

The incoming end of the trunk-line at the trunking-board is providedwith a terminal plug, which is shown inserted in the springjack of atelephone-line, the two telephonelines being thus united through thetrunkline and the connection appliances at the two s'witchboards.

The switchboard-A is the answering or longdistance board. Theswitchboard B is the trunking-board. The trunk-line extends in two limbs1 2 from a spring-jack a at the answering-switchboard to a terminal plug6 at the receiving-board. The A operator is provided with apparatusforconnecting lines together, which consists of a pair of plugs c d unitedby link conductors 4 5 of aplug-circuit. A calling-key e is associatedwith the plugeircuit and is adapted when depressed to sever the linkconductors uniting the two plugs and to ground the tip of thecalling-plug (Z.

The trunk-line is divided at the switchboard B by a repeating-coil g,the windings g g of said repeating-coil being connected in the circuitof the trunk-line leading to the A board and the windings g connected inthe circuit leading to the trunk-plug 1).. The circuit of the trunk-linefrom the windings g g of the repeating-coil to the trunk-plu g b iscontrolled by the armatures it if of the relay or electromagneticcalling-key it. These armatures of the calling-key are connected withthe two lineterminals of the trunk-plug, and the back contacts of saidarmatures are connected with the windings g g* of the repeating-coil g.The front contacts of the armatures are connected to the poles of asource of callingcurrent Z; The relay h is thus adapted when energizedto sever the trunk-line and connect the terminals thereof leading to thetrunk-plug with the circuit which includes the calling-generator 7c.

A. local circuit for the relay it, including the central battery 2', isprovided at the trunkingboard. This local circuit is controlled by thearmature and front contact of a differential relay m. This relay m isprovided with two differential windings connected together to earththrough the armature and back contact of a relayl and the winding of arelay '72,. The other ends of the diflerential windings of the relay mare connected, respectively, with l the two limbs 1 2 of thetrui'ik-line through the windings y" of the repeating-coil.

The usual supervisory relay 0 1s provided on one side of the trunk-linebetween a pole of the battery 1 and a terminal piece of the trunk-plug.The armature of this relay is adapted when drawn up to close the circuitol a branch conductor (3 from the tree pole of the grounded battery 1'to earth through the winding of the relay so that when the calledsubscriber responds by taking his telephone from its switch-hook, and socloses a brid e of the line at the substation, the supervisory relay 0in drawing up its armature will close a local circuit through the relayand break the circuit of the ground branch, which includes the relay u.The latter relay controls a disconnect signal-lamp I, which is lightedwhen the relay is inert.

\Vhilc two batteries (marked 1' and I) are shown in the drawing, it willbe understoml that in accordance with the usual practice but a singlebattery may be employed, connected as indicated At theansweringswitchboard the limbs l 2 of the telephone-line are connectedtogether through impedance-coils r to a conductor 7, which extends tothe t'ree pole of a grounded battery The conductor 7 includes thewinding of a relay 1' and is itself controlled by the armature and frontcontact of a relay s. The relay s is included in a local circuit 8 frombattery 7), established in registering contacts of the plug and thespringjack of thetrunk-line. A signal 1/ is included in the portion ofthis local circuit 8, which is associated with the plug (Z, and aresistance r is included in the portion of said circuit which isassociated with the spring-jack ol the trunkline. The relay 1* isprovided with switchcontacts which control a short circuit of theresistance a, so that when the relay is excited said short circuit isclosed. The relay a, which is also included in the local circuit 8, isadapted to respond to current l'rom the battery 1;) whether theresistance 1* be short-circuited or not; but the signal 1/ is adapted torespond only upon the increased current when the resistance r isshort-circuited by the relay r.

The operation of the system is as follows: \Vhen the connection is lirstmade from the answering-board to the called line through the trunk-line,the circuit of the grounded battery 1) is closed by relay s through theimpedance-coils 1 (I to the limbs 1 2 ol the trunk-line in multiple,through the dill'erential windings of the relay in in multiple, and toground by way of the back contact of relay 1, which is not yet excited,and the winding of relay 12. The ellects ol the two windings of relay mneutralize one another, so that the armature of said relay [is not Relay11 1s excited and shunts drawn up.

out its controlled signal-lamp, The A operator Wishing to signal thecalled party depresses her calling key 6', thereby putting a groundconnection on the limbl of the trunkline by way of the tip or thecalling-plug 05. Current from battery 19 then divides at theimpedance-coils go, as before; but the portion of the current whichpasses to the conductor 1 passes directly to earth at the contact of thecalling-key 0 instead of flowing out over the trunk-line. The portion ofthe current which passes to conductor 2 flows through one ofthe windingsof relay m and then divides, one part passing to earth through the relaya and the other part passing through the other winding of magnet m (in adirection to augment the effect produced by the current in thefirst-mentioned winding) and back over limb 1 to earth at thecalling-key c. The relay m therefore draws up its armature and closesthe local circuit of battery 6 though the electromagnetic calling-key72,, which attracts its armatures 72, [L2 and connects theringing-generator to the terminals of the trunk-plug 5, and so with thecalled line. Sufficient current still flows through the relay n toexcite it and prevent the display of the disconnect-signal. Thelong-distance operator at the A board may thus ring the called stationas long or as frequently as desired without being obliged to call uponthe B operator for this purpose. When the called party responds, thearmature of relay 0 is drawn up and closes a local circuit through therelay Z, which breaks the earth connection of the windings of thedifferential relay m and connects the relay n in a local circuit withbattery 71 to maintain the same excited. The trunk-line is thus freedfrom connection with the earth at the B switchboard during conversation:

The operator at the A switchboard supervises the connection and receivesthe disconnect-signals when the conversation is finished. After theconnection has been put up and until the called party responds thecircuit of battery 10 will be completed through the relay 1? to earth atthe B switchboard by way of the armature and back contact of the relayZ. Upon the response of the called party, however, the relay Z, beingexcited, breaks this circuit, so that the relay risdeenergized andallows its armature to fall back, thus opening the short circuit aboutthe resistance '0. The current through signal a being out down by theintroduction of this resistance 0 into the circuit, said signal becomesinert and remains inert during the conversation. When, however, thecalled party hangs up his telephone, the supervisory relay 0 at theswitchboard B will be deenergized, breaking the circuit through therelay Z, whereby the armature of the last-mentioned relay is permittedto fall back and reestablish the circuit from battery 12 through therelay r over the trunk-line to earth. Relay r shortcircuits theresistance '0, which is included in the circuit of the signal at, sothat the signal responds to the increased current and displays adisconnect-signal. A clearing-out annunciator-drop -is also provided ina bridge of the A operators plug-circuit to receive a disconnect-signalfrom the substation of the calling-line.

When the A operator in response to the disconnect-signal removes theplug from the trunk-line jack, the battery connection with thetrunk-line is broken at the switch-contacts of the relay 8, and therelay n is deprived of current, so that it allows its armatureto fallback and open the shunt around the disconnect-lampt at the Bswitchboard. Said lamp 2, thus receives current for its illumination andindicates to the B operator that the trunk connection may be taken down.

Having th us described my invention, I claim as new, and desire tosecure by Letters Patent, the following:

1. The combination with two telephoneswitchboards and telephone-linescentering at each board, of a trunk-line extending between the boardsand means at each board for connecting the trunk-line to other lines, arelay at one of the boards, a source of calling-current and meanscontrolled by said relay for applying the calling-current to thetelephoneline which is connected with the trunk-line at that board,differential windings for said relay connected respectively with thelimbs of the trunk-line, means for producing aflow of current in bothlimbs of the trunk-line, and a switch at the distant end of thetrunk-line for diverting current from one of the differential windingsof the relay, substantially as set forth.

2. The combination with a metallic-circuit telephonetrunk-line, of anelectromagnetic calling-key at one end thereof, a local circuit for saidcalling-key including a source of current, a relay controlling the saidlocal circuit,

differential windings for said relay connected respectively with the twolimbs of the telephone-line, means for producing a flow of current inboth limbs of the trunk-line, and

a switch at the distant end of the trunk-line adapted to alter the flowof current in one of the differential windings of the relay, as byshunting the same, whereby the calling-key at one end of the trunk-linemay be actuated by moving the switch at the distant end, substantiallyas set forth.

3. The combination with two switchboards and telephone-lines centeringat each board, of a metallic circuit trunk-line extending between theboards and means at each board for I nected With the two limbs of thetrunk-line, respectively, and with a return-conduetor, as the earth,means for producing a flow of current in both limbs of the trunk-line,and a switch at the board distant from the callingkey, controlling theconnection of one limb of the trunk-line circuit with the earth or otherreturn-conductor, whereby the calling-key may be actuated from thedistant board, substantially as set forth.

4. The combination with a metallic-circuit telephone trunk-line, of anelectromagnetic calling-key at one end of the trunk-line, a localcircuit for said calling-lrey including a source of current, a relaycontrolling the said local circuit, difl'erential windings for saidrelay connected respectively with the two limbs of the telephone-lineand having a common earth connection, a grounded source of current atthe distant end of the trunk-line connected with the two limbs thereofin multiple, impedance-coils q q interposed between the two limbs of thetrunk-line and a source of current, and a switch 6 adapted to connectone of the limbs of the trunk-line to earth, whereby the differentialrelay may be excited and the calling-key actuated from the distant endof the trunk-line.

5. The combination with a metallic-circuit trunk-line, of a callingdieyatone end thereol', an electromagnct for actuating the callingkey, twodiiierential windings for the magnet connected respectively between thetwo limbs of the trunk-line and a third conductor, said third conductorextending to the distant end of the trunk and there being connected withthe two limbs of the trunk-line, a source of current in the circuit ofthe third conductor, a switch in the circuit of the third conductor atone end of the trunk-line, a signal device in the third conductor at theother end of the trunk-line, said signal device being controlled by saidswitch, and a second switch at the end of the trunk-line distant fromthe calling-key, adapted to effect the actuation of the callingkcy byaltering the flow of current in one of the windings of itscontrol]ing-magnct, whereby the calling-key and the signal device may beindependently operated.

In witness whereof I hereunto subscribe my name this 27th day ofJanuary, A. .l). 1902.

HENRY M. CRANE.

itnesses:

Pnnsco'r'r H. CooLIDen, HENRY F. \Vnrrn.

